Lance-type liquid reducing agent spray device

ABSTRACT

A lance-type spraying assembly for directing a reducing agent into a combustion zone or discharging combustion gases for Nox emission control. The spraying assembly including a lance body having an inlet end and a downstream end and a spray nozzle arranged at the downstream end of the lance body. The lance body includes an air passage for connection to an air supply, a liquid reducing agent supply passage for connection to a liquid reducing agent supply and a liquid reducing agent return passage. The liquid reducing agent supply passage communicates with the spray nozzle. The liquid reducing agent return passage communicates with the liquid reducing agent supply passage near the downstream end of the lance body for recirculating a portion of the liquid reducing agent and extends near the liquid reducing agent supply passage along at least a portion of the length thereof in order to help cool the liquid reducing agent therein. The liquid reducing agent return passage is sealed against the spray nozzle. The air passage extends near at least a portion of the liquid reducing agent supply passage in order to help cool the liquid reducing agent therein.

FIELD OF THE INVENTION

The present invention relates generally to devices for controlling NOxemissions in combustion processes, and more particularly to a spraydevice or system for directing a reducing agent, such as urea, into acombustion zone or discharging combustion gases for NOx emissioncontrol.

BACKGROUND OF THE INVENTION

NOx emissions are a product of combustion processes and contribute tomajor pollution problems such as acid rain. Two processes forde-nitrification are SNCR (Selective Non-Catalytic Reduction) and SCR(Selective Catalytic Reduction). Both processes commonly use ammonia asa reducing agent in the de-nitrification process of converting NOx intonitrogen and water vapor.

With the SNCR (Selective Non-Catalytic Reduction) process, ammonia isinjected directly into combustion flame at temperatures that range fromabout 878 to 1158 degrees C. (1600 to 2100 degrees F.). The ammoniadirectly reacts with the NOx, reducing the emissions by 30–70%.

With the SCR (Selective Catalytic Reduction) process, ammonia vapor isinjected into the flue gas stream at temperatures from 318 to 430degrees C. (600 to 800 degrees F.). The gas then passes over a catalystwhere the reaction occurs reducing the emissions by 80 to 90%. In thisprocess, atomization and control of droplet size are critical to thereaction process because of the reduced reaction temperaturenecessitated by the operating temperature of the catalyst.

In both reduction methods an injection system for the ammonia is used.Because of the higher operating temperatures with the SNCR process,hydraulic nozzles can be used without the necessity for pressurized airatomization of the liquid reducing agent. In such SNCR processes,hydraulic nozzles are mounted on lances that extend into the combustionflame. In the SCR process, air-atomizing nozzles are mounted on lancesthat extend into the discharging gas stream. Because of the lowertemperatures at such location, the injection device must supply smalldroplets that vaporize quickly.

Safety concerns with anhydrous and aqueous ammonia has increasedinterest in using urea as a safe and economical alternative. The majorproblem with urea is that it is temperature sensitive. The temperatureof the urea must be maintained below 70° C. (158° F.) prior toatomization and direction to avoid crystallization. If the ureacrystallizes due to prior exposure to high temperatures it will clog theinjection piping and discharge orifices. Atomization and control ofdroplet size also are critical to the reaction process because anycrystallization of the urea prior to atomization and discharge isdetrimental to reaction process.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spraying systemfor direction of temperature sensitive reducing agents, such as urea,for NOx emission control in combustion processes which preventscrystallization of the urea that might impede the flow and atomizationof the reducing agent. More particularly, the invention relates to aspecially designed lance-type spray device which recirculates thereducing agent, i.e. urea, to keep it below its crystallizationtemperature prior to atomization and discharge. Urea that is notatomized and discharged is returned to a supply vessel, where it iscooled and then fed to the directing lance in a recirculating loop. Theurea itself is used as a cooling medium. The lance can be fitted withhydraulic or air atomizing nozzles depending on the process, SNCR orSCR. The lance also can be fitted with additional cooling meansdepending on the application, such as a liquid cooling jacket, a coolingair discharge tube, a vacuum insulator jacket, or an insulation jacket.

The invention further can be used in other elevated temperatureapplications, such as gas cooling and conditioning. Nor is the inventionlimited to urea atomizing/injection applications.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of an illustrative lance-typeurea-spraying device in accordance with the invention with the spraynozzle assembly shown in phantom, removed from the device;

FIGS. 2 and 3 are enlarged fragmentary sections of the lance shown inFIG. 1;

FIG. 4 is an enlarged longitudinal section of the illustrated spraynozzle assembly;

FIG. 5 is a longitudinal section of an alternative embodiment ofurea-direction device in accordance with the invention;

FIGS. 6 and 7 are enlarged fragmentary sections of the lance shown inFIG. 4;

FIG. 8 is an enlarged side view of the illustrated spray nozzle of thedevice shown in FIG. 5;

FIG. 9 is a longitudinal section of still another alternative embodimentof urea-directing lance in accordance with the invention;

FIGS. 10 and 11 are enlarged fragmentary sections of the lance shown inFIG. 7;

FIG. 12 is a longitudinal section of another alternative embodiment oflance in accordance with the invention;

FIGS. 13 and 14 are enlarged fragmentary sections of the lance shown inFIG. 10;

FIG. 15 is a longitudinal section of still another alternativeembodiment of lance in accordance with the invention;

FIGS. 16 and 17 are enlarged fragmentary sections of the lance shown inFIG. 13;

FIG. 18 is a longitudinal section of another alternative embodiment oflance in accordance with the invention; and

FIGS. 19 and 20 are enlarged fragmentary section of the lance shown inFIG. 16

While the invention is susceptible of various modifications andalternative constructions, certain illustrative embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific forms disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now more particularly to FIGS. 1–3 of the drawings, there isshown an illustrative lance-type spraying device 10 for directing liquidreducing agents, such as urea, into a combustion zone or dischargingcombustion gases for controlling NOx emissions. The spraying device 10includes a lance body 55 that has an elongated urea feed tube 11 havingan inlet fitting 12 at an upstream end for connection to a urea supplyand a downstream end connected to a nozzle holder 14 which supports anozzle 15. The nozzle 15 in this case is an air atomizing spray nozzleassembly which utilizes pressurized air to break down and direct aliquid flow stream as an incident to spraying. The nozzle assembly maybe of a known type for directing the desired discharging spray pattern,such as the air assisted spray nozzle assemblies offered by SprayingSystems Co. Preferably, the spray nozzle assembly may be of a typedisclosed in provisional patent application Ser. No. 60/378,337 filedMay 7, 2002, assigned to the same assignee as the present application,the disclosure of which is incorporated herein by reference. Such nozzleassembly, as depicted in FIG. 4, includes a nozzle body 16 threaded intoa central passageway in the nozzle holder 14 and which defines a liquidpassage 18, and an air cap 19 secured to the nozzle body 16 by aretaining ring 20 into which atomizing pressurized air streams aredirected through air passages 21 in the nozzle body, as will becomeapparent.

Urea directed into the inlet fitting 12 is communicated through the feedtube 11 into and through the nozzle 15. As indicated previously, urea ishighly temperature sensitive and will crystallize and clog the sprayapparatus at temperatures far below those occurring in the environmentof combustion processes with which NOx emission control equipmentcommonly is used.

In accordance with the invention, the lance-type spraying device isdesigned to maintain a liquid reducing agent, i.e., in this case urea,at temperatures for optimized atomization and direction, withoutpremature crystallization. To this end, only a portion of the ureasupplied to the nozzle is discharged with the remainder of the ureabeing recirculated to be urea supply along a passageway encompassing thefeed tube. In the illustrated embodiment, the urea supply tube 11 isdisposed within a urea return tube 25 which together define an annularurea return passage 26 for excess urea directed to the nozzle 14. Theurea return tube 25 in this case is fixed in sealed relation at itsdownstream end to the nozzle holder 14 and has one or more radialpassages 28 adjacent its downstream end which communicate with thereturn passage 26.

It will be seen that urea directed through the feed tube 11 in part willbe directed into and discharge from the spray nozzle 14, and in part, byreason of the liquid back pressure, will be directed through the radialpassages 28 and into the return passage 26. Urea entering the returnpassage 26 is forced through the return tube 25 to a urea return fitting29 adjacent an upstream side of the urea feed inlet 12. The urea feedtube 11 in this case extends in sealed relation through the fitting 29.It will be appreciated that urea may be directed from the return fitting29 to the liquid supply which may be maintained at a predeterminedtemperature for supplying urea to the feed tube 11. Hence, recirculationof a portion of the liquid reducing agent about and substantially alongthe length of the urea feed tube 11 itself provides a cooling medium toprevent overheating of the urea prior to atomization and discharge fromthe spray device.

In carrying out the invention, the lance-type spray device 10 isdesigned such that atomizing air directed to the spray nozzle 14functions as a further cooling medium for the urea for maintaining thefeed liquid within an acceptable temperature range for effectivespraying. To this end, the spray device 10 includes an air atomizing airtube 32 mounted in concentric surrounding relation to the urea returntube 25 for defining an annular atomizing air passage 34 which extendsalong a substantial length of the urea return tube 25. The atomizing airtube 32 has a downstream end fixed in sealed relation adjacent thenozzle holder 14 and an upstream end which has an atomizing air inletfitting 35. The atomizing air tube 32 in this case has an upstream endplate 36 through which the urea return tube 25 extends in sealedrelation. Atomizing air directed to the inlet fitting 35 will passthrough the atomizing air passage 34 through passages in or adjacent thenozzle holder 14, and communicate with the air passages 21 in the nozzle15 for intermixing with, atomizing and assisting in direction of thedesired discharging liquid spray. It can be seen that the atomizing airitself becomes an additional cooling medium for insulating the liquidurea directed through the spray device from the high temperaturesassociated with the combustion process.

In further carrying out the invention, the illustrated spray device 10has an external cooling jacket 40 which includes an elongated liquidcooling jacket tube 41 disposed in concentric relation about asubstantial length of the atomizing air tube 32 for defining anelongated liquid cooling chamber 42 about a substantial length of theatomizing air tube 32. The liquid cooling chamber 42 has end plates 44,45 with a cooling liquid inlet fitting 46 which in this case has atubular extension 48 for emitting cooling liquid at a locationintermediate the ends of the cooling chamber 42. The cooling liquidflows in surrounding relation about the length of the atomizing air tubeand is returned in circulating fashion to the cooling liquid supplythrough a return fitting 49, which in this case is located in the sameend plate 44 as the inlet fitting 42.

From the foregoing, it will be seen that during operation of thelance-type spray device, simultaneous with the feed of the liquidreducing agent, namely liquid urea, through the feed tube 11,recirculating travel of the liquid urea through the urea return tube 25,combined with the flow of atomizing air and a cooling liquid through theconcentrically mounted atomizing air tube 32 and liquid cooling jackettube 41 effectively insulate the feed liquid from high temperaturesassociated with the combustion process for preventing crystallization ofthe urea prior to atomization and direction from the spray device.

It will be understood by one skilled in the art that advantages of thepresent invention may be obtained in various alternative embodiments ofspray devices, as described below, where items similar to thosedescribed above have been given similar reference numerals. Withreference to FIGS. 5–8, there is shown an hydraulic spray device 50 inwhich liquid, i.e. urea, is directed through a hydraulic spray nozzle51, with excess feed liquid being recirculated through the urea returnpassage 26. For further cooling and insulating the feed liquid, coolingair in this instance is directed through a cooling air tube 32 supportedin concentric surrounding relation to the urea return tube 25. Thecooling air passes from an inlet fitting 35 adjacent an upstream end ofthe spray device 50 through the air passage 34 and discharges in axialsurrounding relation to the liquid discharging spray. The illustratedliquid spray nozzle 51 is of a known spiral type, such as commerciallyavailable from Spraying Systems Co. under the trade name “SPIRAL JET.”

Referring now to FIGS. 9–11, there is shown another alternativeembodiment of spray device 60 in accordance with the invention, which issimilar to the embodiment of FIGS. 1–4 except that it includes a vacuuminsulator jacket 41 in lieu of a liquid cooling jacket. A vacuum, drawnthrough a fitting 46 in an end wall 44, in this case creates the outervacuum insulating layer about the atomizing air tube 32, urea returntube 25, and urea feed tube 11.

With reference to FIGS. 12–14, there is shown an air atomizing spraydevice 70, similar to FIG. 1, without the liquid cooling jacket. In thiscase, cooling and heat insulation of the feed liquid is achieved solelyby the recirculating liquid urea and by the atomizing air flow.

With reference to FIGS. 15–17, a further alternative embodiment of spraydevice 80 is provided, which is similar to FIG. 1 but uses an insulationjacket 40, in lieu of a liquid cooling jacket. In lieu of a coolingliquid, a solid insulating material 81 is provided within the jacket 40.

Finally, with reference to FIGS. 18–20, still another alternativeembodiment of lance-type spray device 90 is shown, which is similar toFIG. 1 but which includes an outer air cooling jacket 40, in lieu of aliquid cooling jacket. In this case, cooling air is introduced throughan inlet fitting 91 adjacent an upstream end of the air cooling jacket40 for flow about and along substantial length of the atomizing air tube32 for axial discharge in surrounding relation to the atomizing airnozzle assembly 14 and the discharging atomized spray.

1. A lance-type spraying assembly for directing a liquid reducing agentcomprising: a lance body having an inlet end and a downstream end; and aspray nozzle arranged at the downstream end of the lance body; whereinthe lance body includes an air passage for connection to an air supply,a liquid reducing agent supply passage for connection to a liquidreducing agent supply and a liquid reducing agent return passage, theliquid reducing agent supply passage communicating with the spraynozzle, the liquid reducing agent return passage communicating with theliquid reducing agent supply passage near the downstream end of thelance body for recirculating a portion of the liquid reducing agent andextending near the liquid reducing agent supply passage along at least aportion of the length thereof in order to help cool the liquid reducingagent therein, the liquid reducing agent return passage being sealedagainst the spray nozzle, and the air passage extending near at least aportion of the liquid reducing agent supply passage in order to helpcool the liquid reducing agent therein.
 2. The spraying assembly ofclaim 1 further including an external cooling jacket surrounding thelance body.
 3. The spraying assembly of claim 2 wherein the externalcooling jacket comprises a liquid cooling jacket.
 4. The sprayingassembly of claim 2 wherein the external cooling jacket comprises avacuum insulator jacket.
 5. The spraying assembly of claim 2 wherein theexternal cooling jacket comprises an insulation jacket.
 6. The sprayingassembly of claim 2 wherein the external cooling jacket comprises an aircooling jacket.
 7. The spraying assembly of claim 1 wherein the liquidreducing agent return passage extends in surrounding relation to theliquid reducing agent supply passage.
 8. The spraying assembly of claim7 wherein the air passage extends in surrounding relation to the liquidreducing agent return passage.
 9. The spraying assembly of claim 1wherein the spray nozzle is an air atomizing spray nozzle and the airpassage communicates with the spray nozzle.
 10. The spraying assembly ofclaim 1 wherein air passage includes a discharge end near the downstreamend of the lance body for discharging air in surrounding relation to thespray nozzle.